Tomatoes Are Growing in Vermont Greenhouses

There’s nothing quite like a totally ripe tomato, picked fresh from your garden or a local farm field.

In Vermont, the window for this experience is pretty short, typically during August and part of September, until the first frost. The next best alternative is a vine-ripe tomato not from the outdoors, but from inside a high tunnel or greenhouse. Growing tomatoes in these protected environments extends the harvest season by several months, from early summer to late fall, and also keeps the crop out of the rain, avoiding diseases that can attack plants and fruits (yes, a tomato is technically a fruit). To have ripe fruit by June, Vermont greenhouse growers start their tomato plants in February and put them in the ground in March.

Let’s take a look at how the process happens by looking at greenhouse tomato production at Walker Farm in Dummerston, Vermont.

Tomato plants have been growing in this greenhouse for about a week, March 25, 2012. The twine hanging down will be used to trellis the plants as they grow, and the black tube will provide irrigation water. Note the yellow sticky card, which is attractive to insects and therefore used to monitor for the presence of pests.

As a result of the benefits of greenhouse production, and strong consumer demand for fresh local produce, there are now several hundred tunnels and greenhouses in Vermont producing more than $3 million of tomatoes each year. (Tunnels are simple greenhouses, for more information on the differences, click this link.)

Worldwide, most production of greenhouse tomatoes uses hydroponics, which involves growing plants in an inert material, like rock wool or peat moss, and then providing water that contains soluble synthetic fertilizers. In Vermont, the vast majority of greenhouse tomatoes are grown in real, live soil, amended with compost and some fertilizer. Most of these greenhouses are managed organically, which means that no synthetic fertilizers are used and pests are controlled using beneficial insects and natural, low-toxicity sprays if needed. That’s good for our environment and our health.

In recent years, growers have adopted grafting as a standard practice to prevent root diseases. This involves growing two sets of plants: one variety with strong, disease-resistant roots, and another with desirable fruit characteristics. The plants are then cut and spliced together so they can grow as one plant.

Each of these pots at Walker Farm contains two tomato seedlings of different varieties that have been grafted together. Once the graft has healed, the protective clips will be removed and the top off the rootstock variety will be cut off, leaving its roots attached to the variety with desirable fruit characteristics. Then the plants will be transplanted into the soil in a greenhouse.

When grown outdoors, wind takes care of tomato pollination, but in the greenhouse growers must vibrate the plants manually to get pollen from the anthers (male parts) to travel to the stigmas (female receptor, connected to the ovary, which becomes the fruit.) This takes time and is not as effective as bumblebees, which many growers bring in to do the job.

Here a bumblebee pollinates a greenhouse tomato flower. Note the small fruit already formed on the previous cluster to the right. Bumblebees are excellent pollinators of tomatoes, whereas honey bees are not. Many Vermont growers purchase a hive of bumble bees to pollinate their crop; a hive lasts about two or three months.

In the greenhouse, all side shoots, or suckers, are removed from tomato plants so they will grow upright with single stem attached to twine using special clips. This upright growth habit makes the best use of the growing space in a greenhouse, versus allowing plants to sprawl on the ground. The fruiting clusters are usually thinned to 4 or 5 fruits each, when the fruits are still quite small, so that production is balanced over the season, and a heavy fruit load early will not reduce the yield of later clusters.

By the end of June, almost all the fruit from the first cluster has already been harvested and the lowest leaves have been removed from the stems to improve air circulation in the greenhouse, which helps reduce leaf and fruit diseases.

What greenhouse crops are your local farmers growing this season? Please feel welcome to leave a comment below with your take on greenhouse and high tunnel vegetable production in Vermont.

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